The functions and settings of a cellular phone are controlled via menu selection. Typically, the device's display unit presents menus and the first required function/setting can be selected by browsing the menus and then possibly set a required value on it. The menus are often arranged in a hierarchy having a base of which there are some main branches (main menus) from which the submenus branch, and possibly more submenus can further branch from these.
From this kind of menu, one can select by browsing with arrow keys to indicate the right function by a cursor or the menu branch indicating it, and by accepting the choice with an acceptance key. The arrow key is typically a thumb-size rocker button positioned over an analog input device, e.g. mini-joystick or button, situated in the center of the cellular phone. This device is based on sensing the forces applied by the user's finger in the x and y directions. While this device is quite satisfactory in terms of pointing function, its use requires dexterity on the part of the user.
Traditional capacitive touch pads, used in large screen applications, cannot be used in small portable electronic products as their size versus resolution ratio limits the accuracy and usefulness of the navigational data output. Their usefulness is further limited by their inability to provide biometric data.
Optical navigation, similar to the traditional capacitive touch pads, is used in large screen applications. For a typical optical mouse navigation sensor, the sensed array of pixels ranges from 16×16 to 32×32 pixels. This is the amount of information needed to accurately correlate one picture to the other. The correlation occurs over a number of different displacement choices. The distance traveled corresponds to the offset needed to obtain the best correlation.
Individual pressure switch sensors typically have a significant capacitance. The data lines take a finite time to settle after the sense line has had its voltage raised. The readout for each row is limited, e.g. 25 kHz and rate per bit limited, 1 Mbit/sec. Accurate optical navigation requires frame rates of about 500 Hz. This means that each frame can only have about 2000 pixels in it. Further, though optical navigation is ideal for a desktop system, it may not be optimal for the mobile electronic market as any input device to a battery operated portable product needs to be small, thin and very low power.
With the optical mouse or optical navigation, there is another technical challenge with respect to the various surfaces that the mouse could be operating upon. As the user could use the mouse on any number of surfaces, correlating and deducing X&Y movement, from the data is very complicated. Very fast frame rates are required along with a sophisticated navigation algorithm to achieve accurate positioning.
Conventional navigation techniques do not adapt well to small screen applications.